Power tools

ABSTRACT

Power driven devices in which a tool is axially impacted via a driver mounted in a reciprocably driven piston. The tool can be intermittently rotated or not, as desired.

United States Patent 1191 Stelljes Feb. 18, 1975 [54] POWER TOOLS 875,869 l/1908 Trott 173/111 x 3,323,601 6/1967 Uebel [73/111 [75] Inventor. ghxa rles R. SteIIJes, Fayetteville, 3,334,694 8/1967 schnemerw l73/m9 3,463,246 8/1969 Bronnert [73/47 3,650,336 3/1972 Koehler 173/1 10 [73] Asslgnee' gz -g i g gg 3,720,269 3/1973 Warner Cl .11 173/48 [22] Filed: Feb. 2, 1973 FOREIGN PATENTS OR APPLICATIONS 195,868 9/1956 Austria 173/109 [21] Appl. No.: 328,916

Primary Examiner-Ernest R. Purser [52] US. Cl 173/48, 173/110, 173/118, Assistant ExaminerWilliam F. Pate, III

173/133, 173/139 [51] Int. Cl B2511 11/12 57] ABSTRACT [58] Field of Search [73/47, 48, 104, 109, I I0,

173M 116 64/29 Power driven devices in which a tool is axially 1mpacted via a driver mounted in a reciprocably driven [56] References Cited piston. The tool can be intermittently rotatedor not,

UNITED STATES PATENTS as desired 720.319 2/1903 Box et al 173/109 8 Claim$,'9 Drawing Figures FATENTED FEB 1 5 SHEET 10F 3 FATENTED FEB! 8 i915 SHEEI 3 OF 3 FIG. 7

POWER TOOLS The present invention relates to power driven devices and, more particularly, to power driven devices for drilling holes in or otherwise working concrete, masonry, and the like by axially impacting a tool against the workpiece, either with or without intermittent rotation of the tool, depending upon the task and the material involved.

One primary object of the present invention resides in the provision of novel, improved power driven devices of the type just described. Such devices are commonly referred to as power hammers or power driven hammers; and this terminology will, accordingly, be employed herein with the understanding that it is intended to be only descriptive and not limiting.

In power hammers as heretofore proposed, tools with one shank configuration are employed if rotation of the tool is wanted; and tools with a different shank configuration are used if axial impact only is desired. This has the disadvantages of requiring two sets of tools, of necessitating a change of tools to shift from one operating mode to the other, etc.

I have now invented novel power driven hammers which are free of the above-enumerated and other disadvantages. In brief, these hammers include a mechanism of the character described in US. Pat. No. 3,650,336 issued Mar. 21, 1972, to Heinrich P. Koehler for POWER DRIVEN DEVICE for impacting a tool and a ratchet mechanism of the character therein disclosed for imparting intermittent rotation to the tool. In the devices described and illustrated in this patent, the motor of the device is connected through a rotary-toreciprocating motion converting mechanism to the impact producing mechanism, which consists ofa reciprocable piston in which a free-floating driver is slidably mounted.

The driver is dimensioned to strike a closed type tool holder to impart axial impacts to a tool in the holder. Controlled flow of air into and out of the piston on opposite sides of the driver produces positive forces for propelling the driver through its working and return strokes and provides cushions which prevent the driver from striking the ends of the piston as it moves backand-forth therein. I

During each cycle of the impact imparting mechanism, the tool socket and the tool mounted therein are rotatably advanced through an angle of preselected magnitude by a novel motion transmitting mechanism driven by the piston. This mechanism is also torque responsive and interrupts the rotary drive connection between the piston and tool socket if the tool binds or sticks.

The rotary motion producing mechanism includes a drive member which is connected to the reciprocable piston by helical splines so that the drive member rotates back-and-forth as the piston reciprocates. This motion of the drive member is converted to intermittent unidirectional rotary motion by a ratchet arrangement which has an input rotatable with the drive member just described. The output member of the ratchet arrangement and, consequently, the tool holder and the tool mounted therein rotate or advance only as the drive member rotates in one of its two opposite directions.

In addition to the components just described, my power driven hammers include a novel selector mechanism with an actuator accessible from the exterior of the casing for moving the input and output members of the ratchet mechanism out of engagement when axial impacting of the tool without rotation is wanted. Thus, by simply moving the actuator from one to the other of two positions, axial hammering alone or axial hammering plus intermittent rotary advance of the tool can be provided.

The novel arrangement just described increases to a maximum the speed and ease with which power driven hammers can be shifted between the two modes of operation. And it also eliminates the need for two sets of tools with different shank configurations to produce the two modes of operation. At the same time the selector mechanism I employ is simple and rugged and, therefore, has a long service life ant is relatively inexpensive to incorporate in a power hammer and to maintain.

One selector mechanism for a power driven impact device which affords a choice between axial impacting alone and axial impacting plus rotation has heretofore been disclosed in U.S. Pat. No. 3,334,694, issued Aug. 8, 1972, to J. L. Schnettler for R OTARY HAMMER. However, the Schnettler mechanism is quite different from that I have invented and could not be used in power driven hammers which employ impacting mechanisms and drives for producing intermittent rotary ad vance of a tool of the character described above.

Aside from those just discussed, the novel power hammers of the present invention have the advantages .of being compact and relatively light and of having good balance due to the manner in which the motor is positioned with respect to the rotary-to-reciprocatory motion convering mechanism. They are also rugged, providing a long service life, and uncomplicated, making them comparatively inexpensive to manufacture and maintain.

Furthermore, the novel hammers of the present invention are highly effective in drilling and like operations because of the intermittent rotation imparted to the tool in conjunction with axial impacts.

Further, the novel closed type tool holder employed in the hammers of the present invention has been found effective in preventing foreign matter from penetrating to the interior of the hammer casing. This also contributes to proper operation of the hammer and to long service life.

One primary object of the present invention was identified above.

Another primary object of the present invention resides in the provision of power hammers with novel, improved mechanisms for providing a choice between axialhammering alone or axial hammering plus intermittent rotation of the tool.

Other important, but more specific objects of the present invention reside in the provision of novel, improved power driven hammers:

l. with a selector mechanism for shifting between different modes of operation which eliminates the need for employing tools with different shank configurations in these modes.

2. with a selector mechanism for shifting between different modes of operation which includes an actuator accessible from the exterior of the tool.

3. with a selector mechanism for shifting between different modes of operation which is simple and rugged and, therefore, relatively inexpensive to manufacture and maintain and which can be added to.

existing designs without major modifications in them.

4. which are particularly effective for drilling holes in concrete, masonry, rock, and the like. I

5. which are compact and relatively light and well balanced.

6. which, apart from the selector mechanism, are rugged and uncomplicated and, therefore, have a long service life and are relatively inexpensive to manufacture and service.

7. which are versatile.

8. which are constructed to minimize the penetration of foreign matter to the interior of the hammer.

9. which have various combinations of the desirable attributes just described.

Other objects and features and additional advantages of the invention will become apparent from the appended claims and as the ensuing detailed description and discussion proceeds in conjunction with the accompanying drawing, in which:

FIG. 1 is a side view of a power driven hammer constructed in accord with the principles of the present invention and equipped with a selector mechanism in accord with that invention for providing a choice between axial hammering and intermittent rotary advance of a tool and axial hammering alone;

FIG. 2 is a longitudinal section through the front end of the power driven hammer of FIG. 1;

FIG. 3a is a fragmentary side view of the mechanism employed in the hammer of FIG. 1 to produce axial hammering and intermittent rotary advance of the tool;

FIG. 3b is a view similar to FIG. 3a but with the selector mechanism operated to interrupt the rotary advance of the tool so that it will only be axially impacted;

FIG. 4 is a pictorial view of a cup-shaped actuator employed in the selector mechanism;

FIG. 5 is a section through the tool taken substantially along line 5-5 of FIG. 2;

FIG. 6 is a view similar to FIG. 2 of a hammer similar to that shown in FIG. 1, but equipped with an alternate form of selector mechanism;

FIG. 7 is a partially sectioned side view of the selector mechanism employed in the hammer of FIG. 6; and

FIG. 8 is a pictorial view of two cam members which are components of the selector mechanism.

Referring now to the drawing, FIGS. 1 and 2 depict a power driven hammer 18 constructed in accord with the principles of the present invention. The major components of hammer 18 include a casing 20 housing a motor drive-connected through a rotary-toreciprocable motion converting mechanism (neither shown) to the piston 26 of an impact imparting mechanism 28 which also includes a free-floating driver 20 slidably mounted in the piston. Driver 30 is adapted to periodically strike and impart an impact to an axially movable tool holder 32 mounted in the forward end of casing 20 and thence to a tool 33 socketed in the tool holder and retained in place by a conventional spring type retainer 34. The tool may also be intermittently rotated or advanced during each working stroke by the piston, which is drive-connected to too] holder 32 through a reciprocable to intermittent, undirectional, rotary motion converting drive mechanism 36. Drive mechanism 36 is also designed to serve an overload function; i.e., to interrupt the drive connection between piston 26 and tool holder 32 if the rotation resisting torque exerted by the tool on the tool holder rises above a predetermined magnitude.

Hammer 18 also includes a novel selector mechanism 37 having an actuator 38 accessible from the exterior of casing 20. With the actuator in one of two positions drive mechanism 36 is operable to incrementally advance the tool 33 in tool holder 32. With the actuator in its other position, continuity in the drive mechanism is interrupted; and tool 33 is, therefore, axially impacted but not rotated.

Hammer 18 also has a pistol grip 39 supporting a switch 40 for controlling the operation of its motor. The details of these components are not part of the present invention and will, accordingly, not be de' scribed herein.

Referring now specifically to FIG. 2, piston 26 is supportedfor reciprocable, rectilinear movement in casing 20 by a piston guide which has not been shown because it is not part of the present invention and because it is described in detail in US. Pat. No. 3,650,336.

Free-floating driver 30, the other component of the axial impact producingmechanism, has a head 42 dimensioned for a sliding fitin the main body portion 44 of piston 26 and a smaller diameter stem '46 dimensioned for a sliding fit in the necked down forward portion 48 of the piston. Driver 30 is extendible from one end of piston 26 into impacting engagement with tool holder 32 as piston 26 moves forwardly (i.e., toward the nose end of the hammer) and displaced toward the rearward end of the piston during the return stroke of the latter by the controlled ingress of air into piston 26 on opposite sides of driver head 42 and the controlled egress of air therefrom.

The tool holder 32 against which driver 30 impacts includes a cylindrical main body portion 50 in which a tool receiving socket 52 is formed and a closed rear wall 54, which prevents foreign matter from penetrating through the tool socket to the interior of casing 20.

Tool holder 32 is mounted for rectilinear movement in tool casing 20 with a flange 56 at its nose slidingly engaging the interior of the casing section. An O-ring 58 disposed in a recess 60 formed in the tool holder nose portion prevents foreign matter from penetrating to the interior of the tool casing around the tool holder. A ring 62 of resilient material is preferably disposed in the forward end of casing 20 in spaced relation to tool holder 32. This ring keeps tool holder 32 from striking and damaging the casing with motor of hammer 18 running and the hammer idling or with no tool in the tool holder.

The main body portion 50 of the tool holder extends into a bore 64 through the output or driven member 66 of a ratchet type, intermittent rotary motion producing mechanism 68 incorporated in motion converting drive mechanism 36. Output member 66 is rotatably mounted in casing 20, but is fixed against axial movement by an annular ledge 70 in the casing and a retainer 72 fitted therein. External splines 76 on the main body portion 50 of tool holder 32 and cooperating internal splines 78 in the bore 64 of driven member 66 connect the tool holder to ratchet output member 66 for rotation therewith.

The motion converting mechanism 36 also includes a motion converting component or drive member 80 having an internal bore 82 through which the forward end portion 48 of piston 26 extends (see FIGS. 2 and 5). Member 80 is rotatably and axially movable in a bore 84 through an annular boss 86 in casing 20.

Helical external splines88 are formed on the forward end portion 48 of piston 26; and cooperating, internal, helical splines 90 are formed in the bore 82 of driven member 80. Accordingly, as piston 26 is reciprocated, it effects an oscillatory or to-and-fro rocking movement of drive member 80 through an angle determined by the configuration of cooperating splines 88 and 90.

The cylindrical input member 92 of a friction clutch 94 is journalled on and fixed to member 80 for rotation therewith. The output member 96 of clutch 94 is similarly journalled on member 80, but is free to rotate rel ative to this member. Clutch output member 96 is also the input or drive member of ratchet-mechanism 68.

Clutch members 92 and 96 are frictionally drive connected by Belleville washers 98 and 100 journalled on motion converting drive component 80 between the clutch elements and frictionally engaging the forward face 102 of input member 92 and the rear face 104 of output member 96. The Belleville washers allow friction clutch output member 96 to slip relative to input member 92 when the tool sticks or is otherwise subjected to a restraining torque of more than a predetermined magnitude.

Ratchet teeth 106 are formed on the forward face 108 of clutch output/ratchet input member 96, and cooperating ratchet teeth 110 are formed on the rear face 112 of ratchet output member 66. Clutch output mem* ber 96 and ratchet output member 66 are biased into driving relationship by a compression spring 114 having one end which abuts friction clutch input member 92. The other end of this spring engages an annular ledge 116 formed in casing 20.

With teeth 106 and 110 engaged, clutch member 96 drives ratchet output member 66 when motion converting component 80 is oscillated or rotated by piston 26 in one direction. However, when output-input member 96 is rotated in the opposite direction by component 80, teeth 106 slide over the teeth 110; and no rotary motion is imparted to output member 66.

The rotary advance is transmitted to too] holder 32 as it is splined to ratchet output member 66. The incremental advance is in turn transmitted to the tool 33 mounted in the tool socket by employing matching configurations in the tool socket and on the shank of tool 33 to connect them for concomitant rotary movement.

When only hammering axial of tool 33 is wanted, the actuator 38 of selector 37 is shifted to the second of its two positions. This moves clutch output-ratchet input member 96 toward the rear of hammer 18 against the bias exerted by spring 114 and holds it there. Accordingly, although input member 96 continues to be rocked or oscillated by motion converting member 80, this rotary motion is not transmitted to tool holder 32 or the tool 33 mounted therein although the tool holder and tool continue to be impacted by driver 30 as piston 26 moves back-and-forth through its impacting and return strokes.

More specifically, the selector mechanism 37 of hammer 18 includes a cup-shaped member 134 (See FIG. 4) surrounding ratchet mechanism input member 96. An inwardly extending, radial flange 136 on member 134 engages the forward face 108 of input member 96 beyond the teeth 106 formed thereon as shown in FIG. 2.

Member 134 is moved toward the rear of hammer 18 to disengage teeth 106 from the teeth on ratchet mechanism output member 66 by rotating actuator 38 (which is a U-shaped hail) from the position shown in FIG. 3A to that shown in FIG. 3B.

Legs 140 of the bail extend through apertures 144 in two shafts or stems 146 (see FIGS. 2 and 5). Stems 146 are mounted in axially aligned apertures 148 on opposite sides of casing 20 for rotation about an axis extending at right angles to the path along which ratchet input member 96 can move relative to output member 66.

Fixed to or integral with and extending inwardly from stems 146 are eccentrics 150, which extend through slots 152 in member 134. Therefore, as bail 38 is displaced to the FIG. 3B position, the rotation of stems 146 displaces member 134 toward! the rear of hammer 18 against the force exerted by compression spring 114, disengaging ratchet input member 96 from output member 66. For the reasons discussed above, the tool holder 32 of hammer 18 and the tool 33 mounted in it then continue to be subjected to axial impacting, but do not rotate.

When intermittent rotation of tool 33 is again wanted, bail 38 is rotated back to the FIG. 3A position. As it is displaced, the cup-shaped member 134 moves forwardly; and ratchet teeth 106 and 110 re-engage so that the ratchet output member 66 and tool holder 32 will be rotatably advanced as piston 26 reciprocates.

A second form of selector mechanism 158 is employed in the hammer 160 shown in fragmentary form in FIG. 5. Because hammer 160 is the same as hammer 18 except for the selector mechanism, the former will be described only as necessary to make clear the construction and operation of the selector mechanism; and those components of hammer 160 common to it and hammer 18 will be identified by the same reference characters.

Selector mechanism 158 includes a ringlike fixed cam 162 surrounding ratchet output member 66. Adjacent fixed cam 162 is a second, also ringlike cam 164, which is both slidable and rotatable in casing 20. The rear face 166 of the movable cam is dimensioned to engage the forward face 108 of ratchet mechanism input member 96 beyond teeth 106.

Cams 1 64 and 162 have cam faces 168 and 170 so configured that, when cam 164 is rotated relative to the fixed cam, it will be displaced toward the rear of hammer 160 against the force exerted by compression spring 114. This displaces ratchet. input member 96 to the rear, disengaging the teeth 106 on the latter from the teeth 110 on ratchet mechanism output member 66 as in the embodiment of the invention described previously to keep rotary motion from being imparted to the tool holder 32 of hammer 160 or to the tool mounted in it.

Cam 164 is rotated to disengage the ratchet mechanism input and output members 96 and 66 in the manner just described by turning a knob 174 located exteriorly of casing 20. Fixed to or integral with knob 174 is a stem or shaft 176 mounted in casing 20 for rotation about an axis extending at right angles to the path along which ratchet input member 96 moves as it is disengaged from and engaged with output member 66. Stem 176 is retained in place by a retainer ring 178 fitted in the stem and by a spring 180 between retaining ring 178 and a ledge 182 in casing 20'.

Also fixed to or integral with stem 176 is an eccentric 184 which extends into a longitudinal slot 186 formed in the periphery of rotatable cam 164.

With knob 174 in the position shown in FIG. 6, pin 188 is biased by spring 180 into a groove 190 in an arcuate boss 192 formed in casing 20, restraining knob 174 against rotation. Ratchet members 96 and 66 are engaged, and the tool (not shown) in tool holder 32 is rotatably advanced as the piston 26 of the impact imparting mechanism reciprocates.

When axial impact only is wanted, knob 174 is pulled away from casing 20, lifting pin 188 out of groove 190 and freeing knob 174 for rotation relative to the casing. The knob is then rotated until pin 188 is aligned with a second groove 194 in boss 192 and seated in the groove by spring 180 to again restrain the knob against rotation.

As knob 174 is rotated, eccentric 184 rotates movable cam 164, causing one of the cam faces 168 formed on it to ride up the associated cam face 170 on fixed cam 162. This displaces cam member 164 toward the rear of the tool.

For example, if knob 174 is rotated in the direction shown by arrow 196 in FIG. 7, movable cam 164 will be rotated in the direction indicated by arrow 198, moving the cam rearwardly as shown by arrow 200.

As cam member 164 engages the forward face of ratchet member 96, the ratchet input member also moves toward the rear of the tool. This separates ratchet teeth 106 from ratchet teeth 110, and the tool in tool holder 32 will be axially impacted but will not be rotated.

When rotary advance is again wanted, the process just described is reversed. Knob 174 is pulled away from housing 20 freeing it for rotation and then turned until pin 188 drops into groove 190 under the biasing influence of spring 180. This allows ratchet spring 114 to bias movable cam 164 forwardly to the position shown in FIG. 6, re-engaging ratchet teeth 106 and 110. This completes the continuity in drive mechanism 36 and the intermittent rotary advance of tool holder 32 and the tool socketed in it is resumed.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by Letters Patent is:

l. A power driven device, comprising: a casing; a tool holder rotatably mounted in said casing; means which can be cycled through impacting and return strokes for imparting axial impacts to a tool mounted in said tool holder; means including a driving member and a driven member having means providing a drive connection therebetween for so connecting said impact imparting mechanism to said tool holder that said mechanism rotatably indexes said tool holder and the tool mounted therein during one of the strokes in each cycle thereof but does not effect rotation of the tool holder in the other of said strokes; and means selectively operable to effect a relative displacement between said driving and driven members which will interrupt the drive connection therebetween so that said tool can be axially impacted without rotating it, said driven member being connected to said tool holder for rotation therewith and being axially fixed relative to said casing, said tool holder and said driving member being axially movable relative to driven member, the means for connecting the impact imparting mechanism to said tool holder including means biasing said driving member toward said driven member to complete the drive connection therebetween, and the means for interrupting said drive connection being arranged to move said driving member away from said driven member against the force exerted by said biasing means.

2. The power driven device of claim 1, wherein the means for interrupting the drive connection between the driving and driven members by moving said driving member away from said driven member includes a member surrounding said driving member and having an inwardly directed flange engageable with said driving member on the side thereof nearest the driven member and means for displacing said flanged member relative to said driven member comprising a member journalled in said casing means for rotation about an axis normal to the path of movement of the flanged member and accessible from the exterior of the casing and an eccentric extending from the inward end of said pin and engaged with said flanged member, whereby said flanged member will be displaced as the member journalled in said casing is rotated.

3. The power driven device of claim 2, wherein the flanged member is cylindrical and surrounds the driv' ing member, wherein there are rotatably journalled members as aforesaid in axial alignment in opposite sides of said casing, and wherein the means for moving the driving member away from the driven member also includes means for concomitantly rotating said rotatably journalled members.

4. The power driven member of claim 1, wherein the means for moving said driving member away from said driven member includes a fixed cam means, rotatable cam means between and engageable with said fixed cam means and that side of the driving member nearest the driven member, there being co-operating portions of said fixed and movable cam means so configured that said movable cam will be displaced relative to said fixed cam and move the driving member away from the driven member as said rotatable cam means is rotated relative to said fixed cam means.

5. The power driven member of claim 4, wherein the means for rotating said actuator comprises a member journalled in the casing for rotation about an axis normal to the path of movement of the driving member and accessible from the exterior of the casing and an inwardly extending eccentric engageable with said rotatably journalled member and said rotatable cam means. i

6. The power driven device of claim 1, wherein the means for drive connecting the impact imparting mechanism to the tool holder includes a frictional drive connection providing means capable of transmitting only forces up to a selected maximum magnitude operatively connected between said impact imparting mechanism and the driving member, whereby the drive connection between the impact imparting mechanism and the tool holder is effectively interrupted while there is a rotation restraining force on said tool holder which exceeds the magnitude of the force which said frictional drive connection is capable of transmitting.

7. The power driven device of claim 1, wherein the means for drive connecting the impact imparting mechanism to the tool holder includes a ratchet means having said driving member as an input and said driven member as an output and means for rotating said driving member back and forth as said impact imparting mechanism moves through its impacting and return strokes, there being cooperating first and second means on said driving and driven members engageable when said driving member is rotated in one direction only to rotatably advance said driven member and said tool holder.

8. A power driven device, comprising: a casing; a tool holder rotatably mounted in said casing which can be cycled through impacting and return strokes to impart axial impacts to a tool mounted in said tool holder; a mechanism for rotatably indexing said tool during only a selected part of the cycle of operation of the impact imparting mechanism which includes torque transmitting driving and driven members and means for disengaging said members when axial impact only is wanted and engaging them when both rotation and impacting is wanted; and a rotationtransmitting, torque release means in series with the mechanism for rotatably indexing the tool for keeping the torque imposed on said tool from exceeding a selected value. 

1. A power driven device, comprising: a casing; a tool holder rotatably mounted in said casing; means which can be cycled through impacting and return strokes for imparting axial impacts to a tool mounted in said tool holder; means including a driving member and a driven member having means providing a drive connection therebetween for so connecting said impact imparting mechanism to said tool holder that said mechanism rotatably indexes said tool holder and the tool mounted therein during one of the strokes in each cycle thereof but does not effect rotation of the tool holder in The other of said strokes; and means selectively operable to effect a relative displacement between said driving and driven members which will interrupt the drive connection therebetween so that said tool can be axially impacted without rotating it, said driven member being connected to said tool holder for rotation therewith and being axially fixed relative to said casing, said tool holder and said driving member being axially movable relative to driven member, the means for connecting the impact imparting mechanism to said tool holder including means biasing said driving member toward said driven member to complete the drive connection therebetween, and the means for interrupting said drive connection being arranged to move said driving member away from said driven member against the force exerted by said biasing means.
 2. The power driven device of claim 1, wherein the means for interrupting the drive connection between the driving and driven members by moving said driving member away from said driven member includes a member surrounding said driving member and having an inwardly directed flange engageable with said driving member on the side thereof nearest the driven member and means for displacing said flanged member relative to said driven member comprising a member journalled in said casing means for rotation about an axis normal to the path of movement of the flanged member and accessible from the exterior of the casing and an eccentric extending from the inward end of said pin and engaged with said flanged member, whereby said flanged member will be displaced as the member journalled in said casing is rotated.
 3. The power driven device of claim 2, wherein the flanged member is cylindrical and surrounds the driving member, wherein there are rotatably journalled members as aforesaid in axial alignment in opposite sides of said casing, and wherein the means for moving the driving member away from the driven member also includes means for concomitantly rotating said rotatably journalled members.
 4. The power driven member of claim 1, wherein the means for moving said driving member away from said driven member includes a fixed cam means, rotatable cam means between and engageable with said fixed cam means and that side of the driving member nearest the driven member, there being co-operating portions of said fixed and movable cam means so configured that said movable cam will be displaced relative to said fixed cam and move the driving member away from the driven member as said rotatable cam means is rotated relative to said fixed cam means.
 5. The power driven member of claim 4, wherein the means for rotating said actuator comprises a member journalled in the casing for rotation about an axis normal to the path of movement of the driving member and accessible from the exterior of the casing and an inwardly extending eccentric engageable with said rotatably journalled member and said rotatable cam means.
 6. The power driven device of claim 1, wherein the means for drive connecting the impact imparting mechanism to the tool holder includes a frictional drive connection providing means capable of transmitting only forces up to a selected maximum magnitude operatively connected between said impact imparting mechanism and the driving member, whereby the drive connection between the impact imparting mechanism and the tool holder is effectively interrupted while there is a rotation restraining force on said tool holder which exceeds the magnitude of the force which said frictional drive connection is capable of transmitting.
 7. The power driven device of claim 1, wherein the means for drive connecting the impact imparting mechanism to the tool holder includes a ratchet means having said driving member as an input and said driven member as an output and means for rotating said driving member back and forth as said impact imparting mechanism moves through its impacting and return strokes, there being cooperating first and second means on said driving and driVen members engageable when said driving member is rotated in one direction only to rotatably advance said driven member and said tool holder.
 8. A power driven device, comprising: a casing; a tool holder rotatably mounted in said casing which can be cycled through impacting and return strokes to impart axial impacts to a tool mounted in said tool holder; a mechanism for rotatably indexing said tool during only a selected part of the cycle of operation of the impact imparting mechanism which includes torque transmitting driving and driven members and means for disengaging said members when axial impact only is wanted and engaging them when both rotation and impacting is wanted; and a rotation transmitting, torque release means in series with the mechanism for rotatably indexing the tool for keeping the torque imposed on said tool from exceeding a selected value. 